This invention relates to high-density data storage media. More particularly, this invention relates to improving the performance of magneto-optical data storage media.
Disk drives have been included as data storage devices in computers for some time. There are various types of disk drives and media. The so-called "floppy" disk is a removable, relatively fragile magnetic data storage medium which has a relatively low data density. Higher data densities are available on so-called "hard" disk drives (also known as "fixed" or "Winchester" drives), which are also magnetic.
Whenever a disk medium is used for the first time, it must be formatted. Formatting involves the testing by the computer of every area of the disk to make sure it can be accurately written to and read from. In addition, sector header information is written to disks which are soft-sectored. If during the formatting process a subdivision (i.e., track, sector or cylinder) of a disk is determined to be defective (i.e., information cannot accurately be written to and read from the subdivision), information is written to the disk to identify the defective subdivision so that it is not used. Formatting can be a relatively lengthy process, and it becomes more lengthy as the density, or data storage capacity, of the disk increases.
Until recently, personal computers and other smaller computers did not have disk drives of such capacity that the time required to format a disk was considered excessive. Recently, however, fixed disk drives for personal computers have become available with storage capacities in the hundreds of megabytes, and format times have increased.
Most recently, optical disk storage media have been introduced. In one type of optical disk, referred to as "magneto-optical", information is stored magnetically, but is written and read with a laser. However, magneto-optical disk drives have longer format times than magnetic disk drives. Formatting a 250-megabyte magneto-optical disk can take several hours, which may be many times the format time for a magnetic disk of comparable capacity. Not only are format times increased for magneto-optical disks but the time needed to store data on such disks is also increased. The reason for these increases is that data cannot be written onto a location on a magneto-optical disk unless that location has first been erased. This differs from a magnetic disk where new data can be written directly over old data, without the need for first erasing that old data. Because disk drives spin continually, and because only one operation can be performed on a particular disk location each time that location passes the read/write head, which is once per disk revolution, it takes up to three full disk revolutions to erase, write on, and verify a magneto-optical disk. Thus, as compared to a hard disk drive, the latency, or rotational delay (the time needed for data to rotate under the head once the head is in position over the appropriate track), of a magneto-optical disk drive is undesirably increased. As a result, the average data transfer rate for storing data on a magneto-optical disk is decreased as compared to the rate of most magnetic hard disks.
In light of the foregoing, it would be desirable to be able to provide a way to format high density data storage media on a time-distributed basis, rather than formatting such media all at once.
It would also be desirable to be able to provide a way to decrease the time needed to store data on a magneto-optical disk, by eliminating the need to erase at the time a write request is made.